WW2: Britain Declares War on Germany to Save Poland

Declaring a war to save Poland as you put it is not an honest representation of the events that have transpired at that time. Many arguments represented here are valid but they just defend the position taken by British government at that time. The simple truth is that for the Germany, (Poland as the weakest country in Europe at that time, in existence for only twenty years with outdated army and already weaken by military conflict between Soviet Russia and Poland) was just a proving ground for the capability of their army, tactics and testing of political waters sort of speak. All the powers of Europe at that time were reluctant to be involved in any major war including the Germany itself.

Emboldened by the weak politics of the western powers (read Czechoslovakia) the next logical step for the expansion was Poland. Not sure what the reaction would be on the part of the western powers they have obtained security in the east by signing Ribbentrop –Molotov pact. The decisive factor in all of this mass was on 12th of September 1939 in Abbeville, a conference in which France and the United Kingdom decided not to help Poland in its fight against Germany. (This is what we mean by saying that Poland was betrayed by France and United Kingdom). This is what have convinced Stalin to move on Poland a week later, not the “Ribbentrop –Molotov pact” and showed the Germany that west is weak and divided. Only a strong political pressure combined with some sort of military action could have changed the course of history as we know it.

Be it as it may, Germany drew a correct assessment of the political situation and the state of western powers (hence the war in the west) and the rest is history.

Would you read "Mein Kampf" Hitler did not plan to attack GB. He was sure that example of power and ability of his Fascist organization will convince British to elect their own Fascist government. Consequently US will became Fascist as well, and after conquering Soviets the whole world will be united. One can say the Europe had a chance to be truly integrated 60 years sooner (common language will be German, I probably will be working in some coal mine if lucky). The problem was Churchill and his ego.
Britain won the war, but it was devastated country with huge debts, disintegrating empire, social unrest, and demobilized millions who expected big social changes. At that time Britain had no abilities to help anyone. It was a great sacrifice on their part to treat decently demobilized Poles.
We should not forget that Poland annexed part of Czechoslovakia when Germans attacked it in 1938.